1. Field of the Invention
The present invention relates to a ribbon cartridge comprising a housing having a bottom half and a top half, a ribbon received in the housing, a driving means for driving the ribbon, the driving means having two cylindrical driving gears rotatably supported in the housing, the driving gears being in engagement with each other for transporting the ribbon in between the driving gears.
2. Description of the Prior Art
Ribbon cartridges containing a ribbon which is normally inked nylon fabric or carbon coated film are currently widely used in computer printers, typewriters, cash registers and other impact printing machines which transfer the printing agent, namely the ink or the carbon, to the printing medium in accordance with the printing mechanism of the printer. The ribbon is normally an endless loop which is transported in and out of the cartridges continuously to allow the printing mechanism to print on a fresh portion of the ribbon to provide clear print images such as text, graphics, etc.
From German Patent No. DE 31 38 828 C2 a conventional ribbon cartridge is known, which has a drive system consisting of two driving gears for transporting the ribbon. The driving gears are rotatably supported in a two-part housing and are in engagement with each other for transporting the ribbon in between said driving gears. The driving gears are rotatably supported on both the bottom half and the top half of the housing, so that their axis of rotation is fixed relative to the housing and therefore relative to each other when the two housing halves have been assembled. Since those driving gears are usually low-cost gears made of synthetic plastic material, problems arise owing to the fixed axis of the driving gears. The pressure on the contacting surfaces of the teeth meshing with each other is not constant over a contacting length in axial direction of the driving gears, so that the ribbon transported between the two driving gears is caused to climb toward the top half of the housing or to slide downwards toward the bottom half of the housing which results in the ribbon being folded or twisted. Thus, the quality of printing can be reduced or even worse the drive system can be jammed or the ribbon may be damaged.